The present invention relates to a device for controlling the transmission of a vehicle, and, more particularly, to a device for controlling the shift timing of the transmission of a vehicle in accordance with the operating conditions of the engine and the vehicle, from the standpoint of maximizing fuel economy and power output performance.
In a vehicle equipped with a manual transmission and a mechanical clutch, the fuel economy is generally expressed by the following formula: EQU Ef=Sv.times.wf.times.et.times.1000/(fb.times.Nr) (1)
where:
Ef is the fuel economy, in km/liter; PA1 Sv is the vehicle speed, in km/hour; PA1 wf is the specific gravity of the fuel, in g/cm.sup.3 ; PA1 et is the mechanical efficiency of the gear train; PA1 fb is the brake specific fuel consumption, in g/PS.hour; and PA1 Nr is the required power, in PS.
In order to maximize the fuel economy, under the condition that the vehicle speed Sv and the required power Nr are constant, it is necessary to minimize the value fb/(wf.times.et). In this case, since the specific gravity of the fuel wf and the mechanical efficiency of the geartrain et can be taken as being substantially constant, regardless of the operating conditions of the engine, it is necessary to minimize the specific fuel consumption fb, in order to maximize the fuel economy.
Now, because the brake specific fuel consumption fb varies in relation to engine speed and engine torque, better fuel economy will be achieved if engine speed is controlled while maintaining the required power. In order to change engine speed while maintaining the vehicle speed Sv and the required power Nr at constant values, it is necessary to change the transmission ratio, i.e. to effect shifting of the transmission. Therefore, if shifts in the transmission ratio are performed properly in accordance with the vehicle load and engine speed, the fuel economy of the vehicle can be improved.